Throttle Body

[A1990]

There has been some recent discussion on the factory use of DAG on our throttle bodies to seal the blades against the bores. My question is when we have our throttle bodies bored to 63mm, what happens to the DAG? Is it removed? Replaced?

Also, speaking of throttle bodies, I have seen some sell that are now 65mm. There has been a lot of talk about not even needing to bore them to 63mm on a stock displacement engine and now we have 65mm.

Just looking for your thoughts on both these topics.

[bdw18_123]

I would also like more info on this DAG stuff. No one seems to know much about it. My throttle body doesn't have it anymore.

Yes, someone please explain this and very good questions. I know for my 350 I decided against going larger TB because it seems only the larger motors benefit from it; worth only about 5 HP on the 350.

As for the DAG, it seems it comes from these urban dictionary terms for dagnabbit:

http://www.urbandictionary.com/defin...term=dagnabbit

[tomtom72]

Check out Jerry's recent post for the chemical make up of "DAG". He posted up in one of rhipsher's threads where he tells us about using the screws from a guitar.

All I think I know is in order for the EEC programing to get a FI motor to start using the IAC to control air intake at start up you have to seal the T/B blades against allowing any air thru the bores. I think??? The DAG is like a gasket that cuts off the air leaking in around the closed T/B blades when we hit the key.

Disclaimer: what I know about EEC systems could be put on the proverbial post card w/enough room for the Gettysburgh address!

I know that Marc ( Mr. Haibeck ) has a solution if your missing the DAG....but I don't know what it is....

[A1990]

I think I understand what DAG is, however, my question if you bore your throttle body to 63mm or 65mm, isn't the DAG gone? The engine builders must be replacing it with something aren't they? If they aren't then how do they simulate the same gasket effect that DAG provides?

[tccrab]

This is from Marc Haibecs' website:

Loss of the Dag coating can cause excess air leakage past the throttle plates and loss of idle speed control range for the engine control system.

I recommend that the LT5 throttle body bores should never be cleaned. In my experience a normally dirty throttle bore causes no problem. In fact a little oily grime around the throttle plates helps seal the throttles to minimize air leakage. It also lubricates the edges of the plates to avoid sticking. If the bore is extremely dirty or you just can resist the urge to clean it, do it gently with a soft dry cloth.

I have tried to reseal throttle plates with little success. The problem has been with poor adhesion to the bore with the sealing material.

When the Dag is no longer effective I improve the fit of the throttle plates to the bores with a polishing process.




TomC
"Crabs"

[Aurora40]

My 63mm TB has no DAG. I did however have lots of problems with idle control and them closing right.

I got started with it when I stupidly cleaned the TB, removing the DAG. I had serious idle problems right after that. At the time I didn't really know how to solve it other than to buy a new TB. The new prices were insanely high so I figured I'd have it ported along with the top end for about the same price.

[A1990]

Originally Posted by Aurora40

My 63mm TB has no DAG. I did however have lots of problems with idle control and them closing right.

I got started with it when I stupidly cleaned the TB, removing the DAG. I had serious idle problems right after that. At the time I didn't really know how to solve it other than to buy a new TB. The new prices were insanely high so I figured I'd have it ported along with the top end for about the same price.

Bob, does your 63mm have problems?

[XfireZ51]

Lgaff and I both have 63mm TBs on 350s. Neither of us have a problem with idle. If you're intending on using a 63mm bore, it makes sense to match the plenum opening for it. If you compare the two, you'll note that the stock plenum bore for the TB is smaller than 63mm which may explain some of the lack of performance improvement when swapping it in.

Does anyone that has upgraded to 63mm TB on a 350 motr with the plenum opened to match have any dyno improvements? The builders I asked said negligible if any and one said 5 hp increase. Still could not find what it does even on the larger motors. I guess it might be difficult for one to have done a dyno before and after just for this mod. It seems the modificaiton is about $350

Open up secondary bores to 63.5mm plus contour and polish inlets $50.00

Bore Throttle Body secondary inlet valves to 63.5mm
and replace blades w/ 63.5mm Brass blades .062” thick $300.00

If it is worth the extra HP, I would not mind having mine done while I am having all the other work done at the same time? I'll ask this builder about the DAG issue too.